1. Field of the Invention
The present invention relates to a method and an apparatus for temporarily compensating for the change in longitudinal dynamics variables in a motor vehicle brought about by a braking intervention of an electronic stability program (ESP).
2. Description of the Related Art
In modern motor vehicles, electronic stability programs (ESPs) nowadays serve in many ways to increase the driving stability of the vehicle and thereby, as a driver assistance system, make an active contribution to driving safety. By targeted braking of individual wheels, ESP systems counteract vehicle skidding in critical driving situations so as thereby to ensure that the driver has control of the vehicle. Both oversteering and understeering of the motor vehicle are prevented by targeted braking of individual wheels.
In order to identify a critical driving situation, the ESP system continuously compares the driver's input with the operating state of the motor vehicle. In this context, steering angle sensors supply information regarding the steering direction desired by the driver, the engine management system supplies information regarding the engine torque requested by the driver, and wheel rotation speed sensors of the antilock braking system and yaw rate sensors supply information regarding the actual driving behavior of the motor vehicle. If a sufficient discrepancy is ascertained between the identified operating state of the motor vehicle and the driver's input, the ESP system intervenes as an assistance system. Oversteering of the motor vehicle, for example, is corrected by braking the front wheel on the outside of the curve, and understeering, for example, by braking the rear wheel on the inside of the curve. Provision can moreover be made that the ESP system also influences engine management, and decreases the engine power output in critical driving situations in order to prevent the drive wheels from spinning.
Especially when the motor vehicle is being driven in a “sport” mode, however, it can be desirable for the motor vehicle to exhibit elevated dynamics. Provision can be made for this purpose for the ESP system to generate a yaw torque in order to make the motor vehicle more agile and in order to prevent understeering. For this, the system brakes wheels on the inside of the curve, thereby producing the desired yaw torque turning into the curve. An intervention of this kind is intended, however, not to be perceptible as such by the driver of the motor vehicle. Braking of the wheels, however, produces not only the desired yaw torque but also a longitudinal deceleration of the vehicle that the driver feels in some circumstances. To prevent this, provision can be made to compensate for a longitudinal deceleration of the motor vehicle, which occurs as a result of a yaw torque braking intervention of the ESP system, by an elevation of the engine torque above the driver's specification by an amount equal to the braking torque. As a result, no perceptible longitudinal deceleration occurs.
For safety reasons, however, the elevation can be permitted only in a few driving situations and even then only in part. The compensation is therefore carried out using, for example, at most 70% of the braking torque and only when drive power is being applied.